U.S. Pat. Nos. 4,270,626; 4,284,163; and 4,298,086, issued respectively on June 2, 1981; Aug. 18, 1981; and Nov. 3, 1981. Each of the aforementioned patents were issued to William C. Pritchett.
The foregoing patents each disclose transducer means for coupling horizontally-directed forces of a seismic vibrator into the earth. Theoretically, if the transducer remains motionless relative to the ground surface during vibration, the maximum vibrational force is being imposed upon the earth on which the transducer is resting.
Initially, seismic devices were utilized with vibrator or impact mechanisms which impose their forces perpendicularly with respect to the means utilized in coupling the transducer into the earth. More recently, both the vibratory seismic generators, as indicated in the above patents, and the impact-type seismic generators are being inclined from the vertical so that they engage the coupling members at an angle other than perpendicularly with respect to horizontal.
The foregoing patents set forth in detail the difficulties encountered when trying to couple the vibratory seismic transducers into the earth. The problem of maintaining the coupling member motionless so that the maximum force is transferred into the earth is very substantial in the impact-type seismic generators due to the large masses involved. For example, in the impact-type seismic generators currently being utilized, a weight of approximately 5,000 pounds is accelerated to a velocity of over 25 miles an hour over a distance of two to three feet into engagement with the coupling member. Manifestly, it will be appreciated that when such weight is being propelled at an angle relative to vertical, a relatively large horizontal force vector is generated onto the baseplate or coupling member. Such horizontal force vector tends to cause the coupling member to move along the surface of the earth with the resulting loss in efficiency of the seismic generator.
Also, problems are often encountered if the coupling member shifts when multiple impactors are used to produce a single shock wave. For example, the travel distance from the release of the impact member to its impact point on the coupling member must remain fixed or the impact members will not strike the coupling member at precisely the same time.